drinks for baby?

I've heard drinks for baby is unnecessary under the age of 1, unless it's for medical reasons I dehydration. I see people are giving sippy cups to their baby so I'm curious what everyone is putting in them! Water? Watered down apple juice? Not bashing anyone, we have sippy cups but to small for a feeding and would like them to try new things but not sure what's ok or how much is ok for a 9 month old! 😊thanks